Gonadotropin secretion is undoubtedly a key element in the reproductive process. Since the mechanisms that regulate gonadotropin secretion during adulthood develop during sexual maturation, this project will probe the ontogeny of these regulatory systems and their cellular and molecular components. In particular, steroidal and non-steroidal regulation of hypothalamic release of GnRH will be examined during infancy and prepubertal periods of development. In vivo techniques have been devised for monitoring hypothalamic release of GnRH and direct effects of gonadal steroids on anterior pituitary gland secretion of gonadotropins during this critical period of development. Experiments have been designed to examine the development of hypothalamic release of GnRH and its relation to LH secretion. In addition, the neurochemical components involved with restraining GnRH secretion during infancy will be examined. In these experiments, the role of endogenous opiates in regulating LH secretion prior to and during the prepubertal period will be examined in the presence and absence of gonadal steroids. To investigate the involvement of catecholamines in initiating postnatal episodic GnRH secretion, studies have been designed to examine their rates of synthesis in discrete hypothalamic regions at different stages of development. Possible steroidal and opiate influences on catecholamine neuronal activity in these same neural tissues will be examined by receptor-binding studies. Finally, we propose to examine the mode of action of androgenic and estrogenic metabolites of testosterone in regulating LH secretion by examining direct hypothalamic and anterior pituitary sites of action. We have chosen the bull calf as a model for the proposed studies since its size during early developmental periods of sexual maturation permits the use of techniques for directly monitoring hypothalamic GnRH release and anterior pituitary gland responses. The proposed research is designed to provide fundamental insights into the mechanisms regulating gonadotropin sectetion with the ultimate goal of contributing information which may be useful in the development of more efficient methods for regulating fertility in humans and milk and meat- producing species.